The invention relates to the control of electric power supplied to a brake mechanism that produces braking force using an actuator in accordance with electric signals corresponding to brake operation amount and to a shift mechanism that changes the shift position using an actuator in accordance with electric signals corresponding to shift operation.
A shift-by-wire shift mechanism is known that changes the shift position of a transmission using an actuator, such as a motor, in accordance with the shift operation by the driver. Likewise, a brake-by-Wire brake mechanism is known that produces braking force using an actuator in accordance with the braking operation by the driver.
For example, Japanese Patent Application Publication JP-A-2004-256013 describes a parking brake apparatus that reliably prevents a brake mechanism portion from being frozen in an activated state. The parking brake apparatus includes: the brake mechanism portion that applies braking forces to the wheels of the vehicle; a brake actuator that actuates the brake mechanism portion; parking brake commanding means for outputting parking brake command signals; outside temperature sensor for detecting the temperature outside the vehicle and outputting outside temperature detection signals corresponding to the detected outside temperature; and controller. When receiving the parking brake command signals, the controller executes a parking brake control which controls the brake actuator such that braking force is produced at the brake mechanism portion. However, when detecting, based on the outside temperature detection signals from the outside temperature sensor, that the outside temperature falls below a freezing point, the controller executes a brake-release control which controls the brake actuator to maintain the brake mechanism portion in a released state even if the parking brake command signals are input.
According to the parking brake apparatus described in the above publication, it is possible to reliably prevent the brake mechanism portion from being frozen in an activated state.
However, if an actuator-driven brake mechanism and an actuator-driven shift mechanism are powered by a common electric power source, if a power failure of the common power source occurs, both the brake mechanism and the shift mechanism are rendered inoperative.
Because the drive wheels can not be locked by the parking lock mechanism and braking force can not be produced at the brake mechanism when the brake mechanism and the shift mechanism are both inoperative, the stationary state of the vehicle may not be maintained despite the driver' attempt to control the shift mechanism or to control the brake mechanism.
Thus, the parking brake apparatus described in the above publication is designed to perform the control that simply releases the parking brake at a low temperature, and it does not address the possibility of power failure of the common power source.